Anchoring in a lightweight building element

ABSTRACT

A method of anchoring a connector in a heterogeneous first object that includes a first building layer and, distally of the first building layer, an interlining layer. The method includes providing the first object and the connector, which includes thermoplastic material in a solid state; contacting the connector with the first building layer; applying a first mechanical pressing force to the connector until the first building layer is pierced by the connector and a distal portion of the connector reaches into the interlining layer; applying a second mechanical pressing force and mechanical vibration to the connector until a flow portion of the thermoplastic material is flowable and penetrates structures of the first object, and a distally facing abutment face of the head portion abuts against the metal profile in a region next to the opening; and letting the thermoplastic material resolidify to yield a positive-fit connection.

BACKGROUND OF THE INVENTION Field of the Invention

The invention is in the fields of mechanical engineering andconstruction, especially mechanical construction, for example automotiveengineering, aircraft construction, shipbuilding, machine construction,toy construction etc. In particular, it relates to a method of anchoringa connector in a first object and of mechanically securing a secondobject to a first object.

Description of Related Art

In the automotive, aviation, furniture and other industries, there hasbeen a tendency to move away from steel constructions and to uselightweight building components. An example of such elements arelightweight building elements that include two outer, comparably thinbuilding layers, for example of a fiber composite, such as a glass fibercomposite or carbon fiber composite, a sheet metal or also, depending onthe industry, of a fiberboard, and a middle layer (interlining) arrangedbetween the building layers, for example a cardboard honeycomb structureor a lightweight metallic foam. Lightweight building elements of thiskind may be referred to as “sandwich boards” and are sometimes called“hollow core boards (HCB)”. They are mechanically stable, may lookpleasant and have a comparably low weight.

However, because the building layers are thin and the interlining is notsuitable for anchoring a connector—such as a dowel—in it, it isdifficult to attach an object to the lightweight building elements otherthan by an adhesive bond to the surface.

To meet these challenges, the automotive, aviation and other industrieshave started heavily using adhesive bonds. Adhesive bonds can be lightand strong but suffer from the disadvantage that there is no possibilityto long-term control the reliability, since a degrading adhesive bond,for example due to an embrittling adhesive, is almost impossible todetect without entirely releasing the bond. Also, adhesive bonds maylead to a rise in manufacturing cost, both, because of material cost andbecause of delays caused in manufacturing processes due to slowhardening processes, especially if the surfaces to be connected to eachother have certain roughness and as a consequence the quickly hardeningthin-layer adhesives cannot be used.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method ofanchoring a connector in a first object, especially in a sandwich boardthat has a comparably weak an interlining layer sandwiched between afirst and a second building layer, wherein the interlining layer may nothave sufficient stability to serve as sole anchoring material for theconnector. It is a further object to provide a method of securing asecond object to a first object. The methods should overcomedisadvantages of prior art methods.

A method of anchoring a connector in a heterogeneous first objectincluding a first building layer and, distally of the first buildinglayer, an interlining layer, wherein the interlining layer has a densitysubstantially lower than a density of the first building layer and/or amechanical resistance against insertion of the connector substantiallylower than the corresponding mechanical resistance of the first buildinglayer, the method including the steps of:

-   -   providing the first object;    -   providing the connector that includes thermoplastic material in        a solid state and extends between a proximal end and a distal        end;    -   bringing the connector into physical contact with the first        building layer;    -   applying a first mechanical pressing force to the connector        until the first building layer is pierced by the connector and a        distal portion of the connector reaches into the interlining        layer;    -   applying a second mechanical pressing force and mechanical        vibration to the connector until a flow portion of the        thermoplastic material is flowable and penetrates structures of        the first object, and a distally facing abutment face of the        head portion abuts against the metal profile in a region next to        the opening; and    -   letting the thermoplastic material resolidify to yield a        positive-fit connection between the connector and the sandwich        board.

In this, the mechanical resistance may, for example, be the force neededto advance the connector by a certain distance (for example 1 mm) intomaterial of the respective material if no additional energy impinges.

The first mechanical pressing force and the second mechanical pressingforce may be identical in magnitude or especially may be different fromeach other in magnitude. Especially, the first pressing force may belarger than the second pressing force.

The second pressing force and/or possibly also the first pressing forcemay be subject to a pressing force profile, i.e. may vary depending ontime and position of the connector relative to the first object. Thepressing force may be controlled depending on the position, on theencountered resistance, and/or on the time.

The second pressing force and in many embodiments also the firstpressing force may be applied by a sonotrode that presses against theconnector and that during the step of applying mechanical vibration(i.e. while the second pressing force is applied) is subject to themechanical vibration that is coupled via a distally facing coupling-outface of the sonotrode into the connector. In many embodiments thesonotrode in this will be in physical contact with the connector,however, it is also possible that an intermediate element is presentbetween the sonotrode and the connector.

In many embodiments, no mechanical vibration will be coupled into theconnector while the first mechanical pressing force is applied to piercethe first building layer. This may especially be advantageous in someembodiments in which a distal end of the connector—that pierces thefirst building layer—includes thermoplastic material. If no vibrationsact during piercing, no softening of the distal end may occur. However,optionally the piercing of the first building layer may be vibrationassisted, i.e. in embodiments, mechanical vibrations act also during thestep of applying the first pressing force. Such mechanical vibrationsmay optionally be different from the vibrations that act during thesubsequent step of applying the second mechanical pressing force inamplitude and/or frequency.

In the step of applying the first pressing force and thereafter, in manyembodiments the first building layer will only be pierced and remains acoherent, contiguous layer. Portions of the first building layer aroundthe piercing location may for example be deformed, such as bent towardsdistally.

Upon further insertion of the connector, the first building layer aroundthe piercing location may become integrated in the anchoring set-up, forexample by the flow portion flowing around it and embedding portions ofthe first building layer around the anchoring location, and/or byguiding the connector and for example even exerting a resilient lateralforce on it that causes some clamping. Thereby, these for portions maycontribute to the stability of the anchoring.

For the step of applying the second mechanical pressing force, thevibrations may be caused to set in from the beginning (i.e. as soon asthe first building layer has been pierced) or only after the distal endof the connector has advanced into material of the interlining layer bya certain minimal distance.

During the step of applying the second mechanical pressing force, atleast a proximally facing coupling face of the connector, via which thesecond pressing force and the vibrations may be coupled into theconnector, will be advanced further into a distal direction, i.e. atleast a portion of the connector will advance further into the firstobject.

The first object may especially be a sandwich board, further including asecond building layer distally of the interlining layer, the secondbuilding layer having a density and/or mechanical stability (especiallyresistance against insertion of the connector) substantially higher thanthe density/stability of the interlining layer.

For example, the second building layer may be of a same composition asthe first building layer. A thickness of the second building layer mayoptionally be a same thickness as a thickness of the first buildinglayer.

Generally, the first object may be a sandwich board in which theinterlining layer has a structure with gas-filled spaces, for example ina regular arrangement. The gas-filled spaces may in embodiments extendvertically between the first building layer and the second buildinglayer. In addition or as an alternative, the gas-filled spaces may takeup a substantial part of the interlayer volume, for example at least 50%or at least 65%. An average density of the interlining layer is forexample smaller than a density of the first and/or second building layerby at least a factor 5, in embodiments at least by a factor 10 or even afactor 15.

Such sandwich boards with optimized thickness ratios (with buildinglayer thicknesses of for example 1-2% of the overall board thicknesseach) may be shown to have a bending stiffness similar to a monolithicboard of the building layer material of a more than five times higherweight. Thus, sandwich boards with sufficiently low interlining layerthickness may bring about substantial reductions in overall weight givena certain mechanical stiffness requirement.

However, if in sandwich boards of this kind a connector (or otherdevice) is driven into the object the mechanical resistancesubstantially drops as soon as the first building layer has beenpenetrated and the connector is to be driven into the interlining layer.In addition, this resistance drop is not fully predictable and dependson whether the distal end of the connector advances in a hollow space ornot. Therefore, after having been driven through the first buildinglayer, the connector may be expected to crash through the interlininglayer and also through the second building layer. However, this willresult in insufficient anchoring of the connector, and often the secondbuilding layer should remain intact.

It is an insight underlying the present invention that it may bebeneficial to nevertheless drive the connector through the firstbuilding layer and at the same time to control the pressing force in amanner that it advances through the interlining layer in a controlledmanner and/or stops before the second building layer may be disrupted.

Especially, in embodiments, the second mechanical pressing force isapplied until a distal end of the connector is sufficiently in contactwith the second building layer for the mechanical resistance to increaseagain, i.e. the pressing force is applied until the connector reachesthe second building layer but without the second building layer beingpenetrated.

For example, the pressing force during the process may be controlled sothat it reaches a first level during the step of piercing the firstbuilding layer, then drops immediately to follow a second profile duringmovement through the interlayer, and reaches a third level when a theadvancing movement is impeded by the second building layer. In this, thefirst level and the third level are above an average pressure valueduring the second profile, for example above any pressure value reachedwhen the second profile is followed. In other words, the pressing forceis high until the first building layer is pierced, then strongly reducedfor the connector to advance into and through the interlining layer, andthen again rises when the connector is in contact with the secondbuilding layer (or an adhesive layer attributed to the second buildinglayer).

In a special group of embodiments, the connector includes a portion of anon-liquefiable material in addition to a thermoplastic portion, whichnon-liquefiable portion forms a distal piercing structure initially, butwhich portion is displaced relative to the thermoplastic materialtowards a proximal direction by the effect of the (second) pressingforce as soon as the thermoplastic material becomes sufficiently softdue to the impact of the vibration energy.

In this text, generally the term ‘connector’ refers to a connector in abroad sense of the word, including a mechanical connector formechanically connecting another object or a connecting portion, i.e. theconnector may be one-piece with the object to be connected orconstituting the object to be connected. Also, the connector maydirectly carry or have integrated such second object (for example if thesecond object is smaller than the connector itself, for example if thesecond object is a sensor, a cable, etc.

In a group of embodiments, the method includes the further step ofsecuring a second object to the first object by means of the connector.For example:

-   -   The connector may include a head portion, and the second object        is clamped between a proximally facing surface portion of the        first object and the head portion.    -   The connector may include an attachment structure, such as a        thread, a structure for a bayonet connection, a clip-on        structure, an attachments surface for gluing a second object        thereto, etc.    -   The second object may be assembled to the first object after        anchoring of the connector from the distal side, for example        through the essentially intact distally facing surface, for        example by being driven into material of the assembly of the        first object and the connector.

In general, the connector may be attached to a second object, prior tothe step of causing mechanical vibration energy to impinge on the firstobject, during/by this step, and/or thereafter.

In embodiments, a second object includes a profile, such as a metalprofile. If applicable, the metal profile may hold the foot.

The method may include carrying out the steps of bringing the connectorinto contact with the first object and of causing mechanical vibrationenergy to impinge on the connector while the object and the connectorare pressed against each other for a plurality of connectors that areall anchored in the same first object simultaneously, for example usinga single sonotrode. In this, the plurality of connectors may be held bya common second object at least during the step of causing mechanicalvibration energy to impinge on the first object while the object and theconnector are pressed against each other.

According to a further, second aspect of the present invention, a methodof fastening a metal profile, for example a metal frame, to a sandwichboard includes using a connector including a thermoplastic material in asolid state and including a head portion and a shaft portion, the methodincluding

-   -   providing the sandwich board and the connector,    -   providing the metal profile with an opening,    -   bringing the connector into contact with the sandwich board        while the metal profile is proximally of the sandwich board,        with the shaft portion of the connector reaching through the        opening;    -   applying a mechanical pressing force and mechanical vibration to        the connector until: the shaft portion of the connector goes        through the proximal building layer and the interlining, a        distal end of the connector is pressed against an inner surface        of the distal building layer, a flow portion of the        thermoplastic material is flowable and penetrates structures of        the sandwich board, and a distally facing abutment face of the        head portion abuts against the metal profile in a region next to        the opening, and    -   letting the thermoplastic material resolidify to yield a        positive-fit connection between the connector and the sandwich        board.

The method according to the second aspect may especially be carried outaccording to the first aspect, i.e. with the step of piercing the first(proximal) building layer by the connector. Any one of theabove-described optional features and embodiments of the first aspectalso apply as options for the second aspect.

The following applies generally, for both aspects:

The structures of the first object penetrated by the flow portion may bestructures, especially pores, of a penetrable material.

A penetrable material suitable for this is solid at least under theconditions of the method according to the invention. It further includes(actual or potential) spaces into which the liquefied material can flowor be pressed for the anchoring. It is e.g. fibrous or porous orincludes penetrable surface structures, which are e.g. manufactured bysuitable machining or by coating (actual spaces for penetration).Alternatively the penetrable material is capable of developing suchspaces under the hydrostatic pressure of the liquefied thermoplasticmaterial, which means that it may not be penetrable or only to a verysmall degree when under ambient conditions. This property (havingpotential spaces for penetration) implies, e.g., inhomogeneity in termsof mechanical resistance. An example of a material that has thisproperty is a porous material whose pores are filled with a materialthat can be forced out of the pores, a composite of a soft material anda hard material or a heterogeneous material in which the interfacialadhesion between the constituents is smaller than the force exerted bythe penetrating liquefied material. Thus, in general, the penetrablematerial includes an inhomogeneity in terms of structure (“empty” spacessuch as pores, cavities etc.) or in terms of material composition(displaceable material or separable materials).

In the example of a sandwich board with glass fiber composite buildinglayers and an interlining between them, the penetrable material may forexample include a foaming adhesive, such as a PU adhesive, between thebuilding layers and the interlining, and/or by the interlining thatitself may include spaces/pores. In addition or as an alternative, thebuilding layers or one of the building layers may be penetrable in theabove sense.

The first object may have a generally flattish section (and may forexample generally be flattish/board shaped) with two opposed broadsurfaces and narrow side faces, the distal and proximal sidescorresponding to the broad surfaces.

The first object, as mentioned, may be a sandwich board, i.e. a buildingelement that includes two outer, comparably thin building layers, forexample of a fiber composite, such as a glass fiber composite or carbonfiber composite, of a sheet metal or also, of a fiberboard, and aninterlining arranged between the building layers.

The building layers may in addition to the mechanically stable compositeor metal sheet also include at least one further material, such as alayer of a plastic material (an example is a mat of PET fibers), barrierfilms (a PP barrier film in an example), etc.; and in addition or as analternative optionally an adhesive layer may be present between thebuilding layers and the interlining layer.

Suitable materials for forming an interlayer, for example in a honeycombstructure, include PP (Polypropylene), PE (Polyethylene), PS(Polystyrene), PET (Polyethylene terephthalate), PA (Polyamide), PC(Polycarbonate), ABS (Acrylonitrile-butadiene-styrene), PPS(Polyphenylene sulfide), PEI (Polyetherimide) as well as otherpolymer-based materials and cardboard. Also a lightweight metallic foamor a polymer foam or ceramic foam, etc., or a structure of discretedistance holders is possible.

The connector includes thermoplastic material. In embodiments, theconnector consists of thermoplastic material.

In other embodiments, the connector in addition to the thermoplasticmaterial includes a body of a not liquefiable material.

Generally, the connector may be essentially pin shaped or bolt shaped(i.e. have a shaft portion), with the mentioned optional head or footportion and/or a possible additional step or taper. Then, an axis of theconnector is caused to extend approximately perpendicularly to the sheetportion and attachment face. However, the connector does not necessarilyhave a round cross section. Rather, it may have a different shape, forexample elongate, polygonal, T-shaped. H-shaped, U-shaped, etc.

The energy applied is mechanical vibration energy. The liquefaction ofthe flow portion in this is primarily caused by friction between thevibrating connector and the surface of the first object, which frictionheats the connector superficially.

In a group of embodiments, the connector and/or a portion of the firstobject against which the connector is pressed comprises, at the surfacethat during the pressing and vibrating is in direct contact with thefirst object, structures serving as energy directors, such as edges ortips, such as energy directors known from ultrasonic welding or for the“Woodwelding” process as for example described in WO 98/42988 or WO00/79137 or WO 2008/080 238.

The first and (if applicable) second objects are construction components(construction elements) in a broad sense of the word, i.e. elements thatare used in any field of mechanical engineering and construction, forexample automotive engineering, aircraft construction, shipbuilding,building construction, machine construction, toy construction etc.Generally, the first object and the connector and (if applicable) thesecond object will all be artificial, man-made objects. The use ofnatural material such as wood-based material in the first and/or secondobject is thereby not excluded. Especially, the second object may be a‘stringer’ or other reinforcement mechanically reinforcing the firstobject (or vice versa).

The flow portion of the thermoplastic material is the portion of thethermoplastic material that during the process and due to the effect ofthe mechanical vibrations is caused to be liquefied and to flow. Theflow portion does not have to be one-piece but may include partsseparate from each other, for example at the proximal end of theconnector and at a more distal place.

In this text the expression “thermoplastic material being capable ofbeing made flowable e.g. by mechanical vibration” or in short“liquefiable thermoplastic material” or “liquefiable material” or“thermoplastic” is used for describing a material including at least onethermoplastic component, which material becomes liquid (flowable) whenheated, in particular when heated through friction, i.e., when arrangedat one of a pair of surfaces (contact faces) that are in contact witheach other and vibrationally moved relative to each other, wherein thefrequency of the vibration has the properties discussed hereinbefore. Insome situations, for example if the first object itself has to carrysubstantial loads, it may be advantageous if the material has anelasticity coefficient of more than 0.5 GPa. In other embodiments, theelasticity coefficient may be below this value, as the vibrationconducting properties of the first object thermoplastic material do notplay a role in the process.

Thermoplastic materials are well-known in the automotive and aviationindustry. For the purpose of the method according to the presentinvention, especially thermoplastic materials known for applications inthese industries may be used.

A thermoplastic material suitable for the method according to theinvention is solid at room temperature (or at a temperature at which themethod is carried out). It preferably includes a polymeric phase(especially C, P, S or Si chain based) that transforms from solid intoliquid or flowable above a critical temperature range, for example bymelting, and re-transforms into a solid material when again cooled belowthe critical temperature range, for example by crystallization, wherebythe viscosity of the solid phase is several orders of magnitude (atleast three orders of magnitude) higher than of the liquid phase. Thethermoplastic material will generally include a polymeric component thatis not cross-linked covalently or cross-linked in a manner that thecross-linking bonds open reversibly upon heating to or above a meltingtemperature range. The polymer material may further include a filler,e.g. fibres or particles of material which has no thermoplasticproperties or has thermoplastic properties including a meltingtemperature range that is considerably higher than the meltingtemperature range of the basic polymer.

In this text, generally a “non-liquefiable” material is a material thatdoes not liquefy at temperatures reached during the process, thusespecially at temperatures at which the thermoplastic material of theconnector is liquefied. This does not exclude the possibility that thenon-liquefiable material would be capable of liquefying at temperaturesthat are not reached during the process, generally far (for example byat least 80° C.) above a liquefaction temperature of the thermoplasticmaterial or thermoplastic materials liquefied during the process. Theliquefaction temperature is the melting temperature for crystallinepolymers. For amorphous thermoplastics the liquefaction temperature(also called “melting temperature in this text”) is a temperature abovethe glass transition temperature at which the becomes sufficientlyflowable, sometimes referred to as the ‘flow temperature’ (sometimesdefined as the lowest temperature at which extrusion is possible), forexample the temperature at which the viscosity drops to below 10⁴ Pa*s(in embodiments, especially with polymers substantially without fiberreinforcement, to below 10³ Pa*s)), of the thermoplastic material.

Specific embodiments of thermoplastic materials are: Polyetherketone(PEEK), polyesters, such as polybutylene terephthalate (PBT) orPolyethylenterephthalat (PET), Polyetherimide, a polyamide, for examplePolyamide 12, Polyamide 11, Polyamide 6, or Polyamide 66,Polymethylmethacrylate (PMMA), Polyoxymethylene, orpolycarbonateurethane, a polycarbonate or a polyester carbonate, or alsoan acrylonitrile butadiene styrene (ABS), anAcrylester-Styrol-Acrylnitril (ASA), Styrene-acrylonitrile, polyvinylchloride, polyethylene, polypropylene, and polystyrene, or copolymers ormixtures of these.

In addition to the thermoplastic polymer, the thermoplastic material mayalso include a suitable filler, for example reinforcing fibers, such asglass and/or carbon fibers. The fibers may be short fibers. Long fibersor continuous fibers may be used especially for portions of the firstand/or of the second object that are not liquefied during the process.

The fiber material (if any) may be any material known for fiberreinforcement, especially carbon, glass, Kevlar, ceramic, e.g. mullite,silicon carbide or silicon nitride, high-strength polyethylene(Dyneema), etc.

Other fillers, not having the shapes of fibers, are also possible, forexample powder particles.

Mechanical vibration or oscillation suitable for embodiments of themethod according to the invention has preferably a frequency between 2and 200 kHz (even more preferably between 10 and 100 kHz, or between 20and 40 kHz) and a vibration energy of 0.2 to 20 W per square millimeterof active surface. The vibrating tool (e.g. sonotrode) is e.g. designedsuch that its contact face oscillates predominantly in the direction ofthe tool axis (longitudinal vibration) and with an amplitude of between1 and 100 μm, preferably around 30 to 60 μm. Such preferred vibrationsare e.g. produced by ultrasonic devices as e.g. known from ultrasonicwelding.

In this text, the terms “proximal” and “distal” are used to refer todirections and locations, namely “proximal” is the side of the bond fromwhich an operator or machine applies the mechanical vibrations, whereasdistal is the opposite side. A broadening of the connector on theproximal side in this text is called “head portion”, whereas abroadening at the distal side is the “foot portion”.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, ways to carry out the invention and embodiments aredescribed referring to drawings. The drawings are schematical in nature.In the drawings, same reference numerals refer to same or analogouselements. The drawings show:

FIG. 1 a setup of for carrying out the method according to the firstand/or the second aspect of the invention;

FIG. 2 a further configuration of a first object, a second object and aconnector during three different stages of a process of securing asecond object to the first object by the connector, wherein the secondobject is a metal frame;

FIGS. 3a and 3b different stages of a process of anchoring a connectorin a sandwich board;

FIG. 4 a process diagram;

FIG. 5 a diagram of the mechanical resistance vs. the depth of thedistal end portion;

FIGS. 6a and 6b an alternative connector and the connector prior tobeing anchored and in an anchored state, respectively;

FIG. 7 a variant of the connector of FIG. 6 a;

FIGS. 8a and 8b yet another connector; and

FIGS. 9a-9d the principle of assisting the anchoring by integratingportions of the first building layer around the piercing location.

DETAILED DESCRIPTION OF THE INVENTION

A set-up for carrying out the method described herein is shown inFIG. 1. The first object 1 is a sandwich board having a first buildinglayer 11, a second building layer 12, and an interlining layer 13, forexample with a honeycomb structure.

The connector 3 has a head portion 31 and a shaft portion 32 ending in adistal tip. The connector may be introduced into the sandwich board bythe distal tip piercing the first building layer 11 as described in moredetail hereinafter, or a whole may be drilled into the sandwich boardprior to the introduction of the connector, the hole extending at leastthrough the first building layer and at most in addition also throughthe interlining layer.

For the fastening process, the sonotrode 6 acts on the head portion 31of the connector 3 and presses it against the inner surface of thesecond building layer that is held against a non-vibrating support (notshown in FIG. 1). The head portion 31 and the first building layer 11 atthe end of the process clamp the second object 2 to secure it to thefirst object.

This is also illustrated in FIG. 2. FIG. 2 also illustrates anadditional step feature 34 that in addition to the flow portion parts atthe distal end (that anchors the connector 3 in the second buildinglayer 12, including possible adhesive etc. and also in the interliningand also may form a sort of a foot portion) causes a proximal flowportion 35 part around the opening in the first building layer 11.

The second object is illustrated to include a metal profile that forms asheet portion 21 around the opening in the first building layer 11. Thesheet portion 21 at the end of the process is clamped between the headportion 31 of the anchored connector and the first building layer.

For penetrating into the first object, the connector 3, the secondobject 2 and the first object are arranged relative to one another sothat the distal end of the connector 3 reaches through a through openingof the second object and is in physical contact with the first buildinglayer 11 (left panel). Then, the connector is pushed through the firstbuilding layer 11 by applying the first pressing force. This may be donevibration assisted (as schematically illustrated in the left panel ofFIG. 2, or without any vibration. As soon as the distal tip of theconnector has pierced the first building layer, the pressing force isstrongly reduced and the connector 3 is moved through the interlininglayer 13. Then, in contact with the second building layer 12, theabove-described process, which results in liquefaction of a flow portion35 of the thermoplastic material, sets in. A non-vibrating support 7 maybe held locally (as schematically illustrated) or extensively againstthe distal surface of the second building layer 12.

FIG. 3a illustrates a set-up similar to the one of the left panel ofFIG. 2 (with no second object shown, however, a second object secured tothe first object may be present or mounted after the process, ofcourse). While the distal side of the first object 1 abuts against astationary support (not shown) the sonotrode 6 is pressed against theproximal incoupling surface of the connector 3 by a driving mechanism42, and, depending on the process stage, a vibration generating device41 (for example including a piezoelectric transducer) sets it intovibrational movement.

A control unit 40 controls the vibration generation and the pressingforce/forward movement.

Generally, in the context of the present, a control unit is a unit inthe functional sense and does not have to be a unit in the physicalsense, i.e. different elements constituting the control unit may bephysically separate from each other and for example belong to differentparts/different entities, which different entities optionally mayinclude further elements and serve further functions.

The apparatus may further include first sensing means for sensingdirectly or indirectly a position of the sonotrode 6 and/or theconnector (a direct sensing means may for example include an opticalposition measuring stage; an indirect sensing means for example may usea control and/or feedback signal of the driving mechanism) and/or asecond sensing means for sensing directly or indirectly a force exertedby the tool on the connector (a direct sensing means may be aforce/pressure measuring device in series with the vibration generatingdevice; an indirect sensing means may use a control and/or feedbacksignal of the driving mechanism and/or of the vibration generatingdevice). The first sensing means and/or the second sensing means may beseparate devices or optionally be integrated in the control unit, i.e.the sensing means may be sensing means in the functional sense of theword, and they do not have to be physically separate entities.

The apparatus may for example be equipped and programmed to control theexerted force and/or the vibration generation according to one of thefollowing criteria:

-   -   According to an option, a pre-defined velocity profile for the        forward movement of the sonotrode may be defined (such as        constant velocity, or a velocity that decreases when the distal        end of the connector is in contact with either of the building        layers). The force needed may then be used as a feedback signal.        -   For example, a trigger force (on the tool) may defined. As            soon as the force exceeds a trigger force, the vibrations            set in.        -   In a variant, a condition for the vibrations to set in is            that both, the trigger force is reached and the position of            the connector is in a certain window. This second option is            suitable for sandwich board first objects in set-ups in            during the piercing of the first building layer the force            exerted on the connector is generally above the trigger            force—and if during this penetration it is not desired that            mechanical vibration energy is absorbed by the system (for            example because it would lead to undesired heat generation            by the connector and/or by portions of the first building            layer).    -   According to another option, the force and/or the vibrations may        be controlled depending on the position, i.e. a        force/vibration-as-a-function-of-position-profile is defined.    -   According to an even further option, if the properties of the        first object are sufficiently precisely defined and well-known,        the force and/or vibration may follow a time-dependent profile.    -   Other options or combinations (for example if the apparatus is        programmed to apply different options for different kinds of        connectors or based on settings chosen by the user) are possible        also.

FIG. 3b depicts the situation after the end of the anchoring process,with the flow portion 35 penetrating structures of the interlininglayer, and possibly also of the second building layer and/or an adhesivelayer connecting these two.

FIG. 4 shows an example of a process diagram. The exerted force 51 issubject to a first peak 51.1 when the first building layer ispenetrated. Then, during penetration of the interlining layer, the forceis lower (51.2) and then again rises as the distal end of the connectorapproaches the second building layer (second peak 51.3). The vibration52 will at least act in this stage when the connector is pressed againstthe second building layer. Optionally, it may also act duringpenetration of the first building layer (first peak, dashed line) orcontinuously starting with the penetration of the first building layer.

As shown in FIG. 4, it may be advantageous if the pressing force ismaintained after the vibrations stop (holding force) until the flowportion has re-solidified at least to some extent.

In FIG. 4, the second force peak 51.3 is illustrated to be lower thanthe first peak 51.1. This does not need to be the case, however. Due toa local deformation at the distal end of the connector by theliquefaction of portions of the thermoplastic material (see for exampleFIG. 8 hereinafter) and/or due to the support by the support surface,the second building layer 12 may in some embodiments even withstand ahigher pressing force than the force needed to pierce the first buildinglayer, in embodiments even if it has the same composition and thickness.

FIG. 5 shows the force F (mechanical resistance against insertion of theconnector; 61) not as a function of processing time but as a function ofthe ‘vertical’ position z. The extension of the first peak 61corresponds approximately to the thickness t of the first buildinglayer. In the intermediate region 61.2, in which the connector advancesthrough the interlining layer, the force may be essentially constant ormay follow some profile (dashed line) that depends on the structure ofthe interlining. When the distal end reaches the second building layer,the force rises again (61.3), for example relatively steeply as shown inFIG. 5. However, if during the transition of the intermediate region(phase 61.2), the connector is advanced only slowly and mechanicalvibrations act, liquefaction or at least softening of distal portions ofthe thermoplastic material may set in already during this phase, and amore smooth transition to higher resistance forces may be observed.

This effect may be used to control the softening profile in a targetedmanner. To this end, use can also be made of the fact that as soon asthe material is above its glass transition temperature, internalfriction caused by the vibration is much higher than below thistemperature, and energy absorption does not require any more externalfriction (with an object, for example the first object, against which itis pressed) to the same degree. This is especially the case if one usesa system with controllable position (such as a servo controlled systemand/or a system with synchronous motor or other motor with preciselycontrolled forward movement).

In embodiments, especially if (for example as illustrated in FIG. 4),the connector absorbs energy and becomes softened already during thepiercing of the first building layer. Specifically, in some embodimentsit can even be observed that the connector at the distal end becomescompletely soft during the piercing step. Nevertheless, absorption (andconsequently heat generation) may take place.

FIG. 6a illustrates a connector with a thermoplastic portion 71 and anon-liquefiable (for example metallic) portion 72. The non-liquefiableportion may be of a particularly hard material and have a distinctpiercing tip at the distal end. During the phase of piercing the firstbuilding layer, the non-liquefiable portion due to this may serve aspiercing aid.

When in a later phase the absorbed vibration energy causes softening ofthe thermoplastic material and ultimately causes the thermoplasticmaterial to become flowable, non-liquefiable portion 72 may be displacedrelative to the thermoplastic portion so that even if the connector ispressed against the second building layer 12 it does not pierce thesecond building layer. To this end, in the illustrated embodiment theproximal end of the non-liquefiable portion is also pointed so as tooffer less resistance against a displacement relative to the softenedthermoplastic material into proximal directions. FIG. 6b shows theresulting configuration.

In embodiments like the one of FIG. 6a , during the phase of piercing,connector may be subject to no vibration energy input or to an inputsufficiently low for the thermoplastic material not to substantiallysoften at the proximal end of the non-liquefiable portion. Duringthe—slow—advancement through the interlining layer, however, theconnector may be subject to vibration energy input so that the materialmay soften until the distal end of the connector races the secondbuilding layer.

A variant of the configuration of FIG. 6a is shown in FIG. 7. In thisvariant, the thermoplastic portion 71 is slitted and formed so that thenon-liquefiable portion 72 widens the slit when displaced towardsdistally (after the thermoplastic material has softened, causing anadditional sideways expansion, as illustrated by the arrows in FIG. 7.

In both, the embodiment of FIG. 6a and the one of FIG. 7, thenon-liquefiable portion 72 may form a distal tip or a distal blade(extending perpendicular to the drawing plane). Similarly, in the otherembodiments described in the present text, the described tips maygenerally be replaced by according blades so that a piercing with acertain extension in one in-plane direction is created.

FIGS. 8a and 8b (FIG. 8b shows a section along the plane B-B in FIG. 8a), show an example of a connector with a tip region of reduced crosssection, in the shown example with an approximately cross shaped crosssection. Such region of reduced cross section area may both, assist thestep of piercing the first building layer and ensure a swift onset ofliquefaction at the distal end as soon as the vibration energy inputstarts so as not to risk that the second building layer is pierced also.

FIGS. 9a and 9b shows a distal end of a connector 3 with a piercing tipin contact with the first building layer 11 of a first object, and FIG.9b illustrates the same detail of the first object after the anchoringprocess. The piercing by the connector 3 will cause the first buildinglayer to become pierced, however, the first building layer 11 remainscoherent, with portions around the piercing location being deformed tobe bent towards distally (downwardly in the orientation of FIGS. 9a and9b ). These deformed portions provide some mechanical resistance againstthe insertion movement of the connector 3, and together with themechanical vibration energy this will cause local heat generation. Theprocess may due to this especially be carried out so that the flowportion 35 includes portions in contact with the first building layer.An at least partial embedding of at the deformed portions of the firstbuilding layer in the flow portion may result, yielding an anchoringeffect around the piercing location, as also shown for example in FIG.3b and in FIG. 6 b.

This effect and the contribution of the first building layer to theanchoring may be used independently of whether there is an additionalanchoring with respect to a second building layer 12, as shown in FIG. 2(middle and right panel) or not.

Similar to what is illustrated in FIG. 2, the connector may includetargeted structure for achieving or intensifying this effect, such asthe step feature 34, or a taper feature, or a collar of energy directors36 located at an axial position where, towards the end of applying thesecond mechanical pressing force and the mechanical vibration to theconnector, the first building layer will be, etc. FIGS. 9c and 9dillustrate an example of a connector 3 with a collar of energy directors36 located at a tapered section. FIG. 9d shows a section along plane d-din FIG. 9 c.

What is claimed is:
 1. A method of anchoring a connector in aheterogeneous first object comprising a first building layer and,distally of the first building layer, an interlining layer, wherein theinterlining layer has a density substantially lower than a density ofthe first building layer and/or a mechanical stability substantiallylower than a mechanical stability of the first building layer, themethod comprising the steps of providing the first object; providing theconnector that comprises thermoplastic material in a solid state andextends between a proximal end and a distal end; bringing the connectorinto physical contact with the first building layer; applying a firstmechanical pressing force to the connector until the first buildinglayer is pierced by the connector and a distal portion of the connectorreaches into the interlining layer; applying a second mechanicalpressing force and mechanical vibration to the connector until a flowportion of the thermoplastic material is flowable and penetratesstructures of the first object, and stopping the mechanical vibrationand letting the thermoplastic material resolidify to yield apositive-fit connection between the connector and the first object;wherein the first mechanical pressing force is lamer than the secondmechanical pressing force.
 2. The method according to claim 1, whereinthe second mechanical pressing force is applied by a sonotrode thatpresses the connector against the first object.
 3. The method accordingto claim 1, wherein the first object is a sandwich board comprising thefirst building layer, a second building layer, and the interlining layersandwiched between the first and second building layers, with a densityof the interlining layer being substantially lower than densities of thefirst and second building layers, and wherein applying the secondmechanical pressing force causes the connector to advance through theinterlining layer until an advancing movement of the connector isimpeded by the second building layer, without the second building layerbeing disrupted.
 4. The method according to claim 3, wherein in the stepof applying the second mechanical pressing force and the mechanicalvibration to the connector, the flow portion of the thermoplasticmaterial is made flowable at an interface between the connector and thesecond building layer.
 5. The method according to claim 3, wherein theinterlining layer comprises gas-filled spaces.
 6. The method accordingto claim 5, wherein the gas-filled spaces take up at least 50% of avolume of the interlining layer.
 7. The method according to claim 3,wherein the density of the interlining layer is smaller than thedensities of the first building layer and of the second building layerby at least a factor of
 5. 8. The method according to claim 3, furthercomprising applying a third mechanical pressing force when the advancingmovement is impeded by the second building layer, wherein the thirdmechanical pressing force is larger than the second mechanical pressingforce.
 9. The method according to claim 1, wherein the connectorcomprises a portion of a non-liquefiable material in addition to athermoplastic portion, which non-liquefiable portion forms a distalpiercing structure initially, but which portion is displaced relative tothe thermoplastic material towards a proximal direction by the effect ofthe second mechanical pressing force as soon as the thermoplasticmaterial becomes sufficiently soft due to the impact of the vibrationenergy.
 10. The method according to claim 1, further comprisingmaintaining the second mechanical pressing force for some time after themechanical vibrations have stopped.
 11. The method according to claim 1,wherein the connector comprises a proximal piercing or cutting shapeincluding a tip or edge.
 12. The method according to claim 1, whereinthe connector comprises a proximal head.
 13. The method according toclaim 1, further comprising carrying out the step of bringing theconnector into physical contact with the first building layer for aplurality of connectors simultaneously.
 14. The method according toclaim 1, further comprising applying mechanical vibration energy toimpinge on the first object while the first object and the connector arepressed against each other for a plurality of connectors simultaneously.15. The method according to claim 13, wherein the connectors are held bya common second object.
 16. The method according to claim 1, and furthercomprising providing a second object, and fastening the second object tothe first object by the connector.
 17. The method according to claim 16,wherein the second object comprises a sheet portion that after anchoringlies against a proximal attachment face of the first object.
 18. Themethod according to claim 17, wherein the sheet portion is clampedbetween the attachment face and a distally facing abutment face of ahead portion of the connector.
 19. The method according to claim 16,wherein the second object comprises a metal profile.
 20. The methodaccording to claim 16, wherein the connector comprises a proximal headportion with a distally facing abutment face, wherein the second objectcomprises a through opening, the method comprising the step ofpositioning the first object, the second object and the connectorrelative to one another so that the second object rests against thefirst object and the connector extends through the opening, with adistal end of the connector being in the physical contact with the firstbuilding layer, and wherein the step of applying the second mechanicalpressing force and the mechanical vibration to the connector comprisesapplying the second mechanical pressing force until a distally facingabutment face of the head portion abuts against the metal profile in aregion next to the opening.
 21. A method of fastening a metal profile toa sandwich board, the method comprising the steps of: providing thesandwich board, the sandwich board comprising two outer building layersand an interlining arranged between the building layers; providing aconnector that comprises thermoplastic material in a solid state andcomprises a head portion and a shaft portion; providing the metalprofile with an opening; bringing the connector into contact with thesandwich board while the metal profile is proximally of the sandwichboard, with the shaft portion of the connector reaching through theopening; applying a first mechanical pressing force to the connectoruntil the shaft portion of the connector goes through the proximalbuilding layer, applying a second mechanical pressing force andmechanical vibration to the connector until the shaft portion goesthrough the interlining, a distal end of the connector is pressedagainst an inner surface of the distal building layer, a flow portion ofthe thermoplastic material is flowable and penetrates structures of thesandwich board, and a distally facing abutment face of the head portionabuts against the metal profile in a region next to the opening; andletting the thermoplastic material resolidify to yield a positive-fitconnection between the connector and the sandwich board; wherein thefirst mechanical pressing force is lamer than the second mechanicalpressing force.